Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$20.48	6.436%	$21.7981	$21.80	$21.80	$21.80
Purchase #2	$91.92	11.425%	$102.4219	$102.42	$102.40	$102.40
Purchase #3	$204.57	10.362%	$225.7675	$225.77	$225.75	$225.80
Purchase #4	$117.86	6.448%	$125.4596	$125.46	$125.45	$125.50
Purchase #5	$206.50	12.172%	$231.6352	$231.64	$231.65	$231.60
Purchase #6	$223.78	13.788%	$254.6348	$254.63	$254.65	$254.60
Purchase #7	$217.48	9.843%	$238.8866	$238.89	$238.90	$238.90
7 purchase totals =	$1,082.59		$1,200.6037	$1,200.61	$1,200.60	$1,200.60